1. Field of the Invention
This invention generally relates to wireless communication systems and more particularly to wireless systems for transmitting data from mobile devices.
2. Description of the Related Art
Communication systems such as wireless systems are designed to meet various demands of subscribers. Service providers continuously seek ways to improve the overall performance of the communication system. As wireless communications become more and more popular for subscribers to obtain data (i.e., email or information from the internet), communication systems must be capable of a higher throughput.
There are two directions of data flow in such systems. Communications from a base station to a mobile device are considered to flow in a downlink direction while the communications originating at the mobile device are considered to flow in an uplink direction. Most of the work in this area has focused on the downlink flow of information, which is to the mobile devices (typically from a base station).
Wireless third generation (3G) communication systems are currently introducing technologies in order to become spectrally efficient, while supporting data services, and in order to provide improved multiplexing voice and multiplexing data services. These efforts have resulted in the development of the 3Gx-EVDV standard, an evolution of the CDMA2000 standard from the 3GPP2 body of standards. Similarly, the Universal Mobile Telecommunication System (UMTS) standard has introduced several advanced technologies as part of the High Speed Downlink Packet Access (HSDPA) specification. An aspect in all of these enabling technologies is to ensure that any associated control information is carried in an efficient manner.
Certain advanced or enabling technologies may include scheduling. Adaptive Modulation and Coding (AMC) and Hybrid Automatic Repeat Request (HARQ) technologies. These technologies have been introduced in an effort to improve overall system capacity. In general, a scheduler, such as is present at a base station (called Node-B in UMTS) selects a user for transmission at a given time, and adaptive modulation and coding allows selection of the appropriate transport format (modulation and coding) for the current channel conditions seen by the user. Accordingly, in scheduling, the Node B grants permission to one or more users at a time, rather than to allow data users to transmit autonomously. Typically, this is based on an estimate of each user's link quality in one of the downlink and uplink.
AMC technologies enable a selection of a data rate and a transmission format (i.e., modulation level and channel coding rate) that best “suits” the scheduled user's prevailing channel condition. Delays and measurement errors result in degraded performance from AMC. So, suppose a block of bits or a packet was sent out using QPSK modulation and a code rate of 0.5 and was received erroneously. A retransmission of that packet takes place, in general with a new appropriate choice of modulation and in general, at least a few new “parity” bits from the original set of coded b its.
HARQ allows combining the original transmission. This greatly improves the probability of correct decoding of the packet. The word “hybrid” in HARQ indicates that Forward Error Correction (FEC) techniques have been used in addition to ARQ techniques. HARQ combining schemes imply that retransmissions are combined with the original unsuccessful transmissions. Accordingly, HARQ helps to ensure that transmissions resulting in unsuccessful decoding, by themselves, are not wasted. Lucent Technologies, Inc.'s Adaptive Asynchronous Incremental Redundancy (A2IR) approach, which is a form of HARQ combining, has been adopted in both the 3G1x-EVDV and HSDPA specifications. A2IR is a flexible approach and allows HARQ combining of copies that use potentially different modulation schemes.
While much of the standardization to date has focused on the downlink (from base station (Node B)) to mobile station, similar enhancements are now being considered for the uplink. The enabling technologies discussed above are also available to enhance the uplink, but the relative importance of these technologies, and the specific methodology for each, may be quite different as related to the uplink. These differences may be due, for example, to different tradeoffs being applicable on the uplink, as compared to the downlink.
The current proposal for uplink data signal format and content does not address all needs for control information in the uplink data transmission. This invention addresses that need by including a new control channel or code in a data signal transmission from a mobile device.